The sisters of murdered Belfast man Robert McCartney challenged the IRA and Sinn Féin last night to break the "climate of fear" they say is preventing anyone from being brought to justice over the killing, after the acquittal of the only man accused of the murder.

At Belfast high court yesterday Mr Justice Gillen cleared Terence Davidson, 51, of murdering McCartney after he allegedly refused to apologise for making a rude gesture to Davidson's wife. The judge at Laganside courthouse, just a block away from Magennis's bar where the alleged fight began, cast doubt over the evidence given by a witness known as C.

Standing just around the corner from the bar, the murdered man's sisters said Sinn Féin should urge its supporters and members to come forward and give evidence against at least nine other men allegedly involved in the fatal attack.

Robert McCartney was murdered by a local IRA gang who had just returned from mourning the dead of another infamous injustice in Northern Ireland - the Bloody Sunday massacre of 1972.

The men who were to murder McCartney, seriously injure the friend he tried to help, Brendan Devine, then forensically cover up their crime and threaten any witnesses had been to Derry on January 31 2005, the 33rd anniversary of the Parachute Regiment killing 13 unarmed civilians.

McCartney's four sisters and fiancee campaigned to bring those responsible to trial. They met the US president, George Bush, at the White House, as part of their crusade to demand that Sinn Féin members came forward as witnesses.

Speaking near where their brother collapsed from his wounds Catherine McCartney, with her sister Paula, vowed that their campaign for justice would not go away. "People can still come forward.

"The police have plenty of intelligence but they lack the evidence to back that up. While the fear still exists we are not going to get justice."

She added: "In this new dispensation Sinn Féin say they are cooperating with the police but in the case I would like to say there is no evidence of that."

She said that the murder of her brother "continues to be an embarrassment to the British and Irish governments and all the powers that be at Stormont", who she said tell the world that Northern Ireland is now free from paramilitarism.

She added: "If there is a new dispensation then prove it by getting those other eyewitnesses to come forward without fear of reprisals."

Sinn Féin and the IRA have always denied the sisters' claims that they were preventing witnesses coming forward.

No witnesses except McCartney's friends Brendan Devine and Ed Gowdy have approached the police with evidence even though the pub was packed when the fight broke out. All of the 72 people drinking there later told detectives they were in the toilet when the assault happened.

Locals in Belfast later remarked that Magennis's Bar should have applied to take its place in the Guinness Book of Records because of the way so many people were packed into the toilets.

Delivering his judgment Mr Justice Gillen praised the witness for being "transparently honest" but cited inconsistencies between how the witness described the alleged attacker's hair and also her inability to identify a weapon.

Earlier the McCartney sisters stormed out of Belfast crown court before the judge delivered his verdict in protest over the press being giving an early copy of the judgment before they learned of it.

Davidson's co-accused, James McCormick, 39, and Joseph Fitzpatrick, 47, were also found not guilty of affray. Fitzpatrick was acquitted on a further charge of assault.

Summing up the judge said: "I recognise that the family of Mr McCartney and others who held him dear will be frustrated and disappointed that whoever it was who cut this young man down in the prime of his life has or have not been brought to justice."

The judge, who sat without a jury, added: "However, the memory of Mr McCartney and the rule of law itself would be ill-served by this court failing to observe the high standards of criminal justice and the burden of proof which prevail in courts in Northern Ireland."

Mr Justice Gillen also warned the three acquitted men that they could yet be brought back to court if more evidence emerges and that the accused in the trial would not be "beyond the reach of potential prosecution".